If I view agg impressions it show like 4xx,xxx but when I click on top channels my highest channel has 9xx,xxx impressions why does it say this?
I would say that your top channel gets shown more than once on some page. The total (519.xxx) is pages. The individual channel is each individual ad. Two ads on one page means twice the channel impression count compared to page impressions.
Each channel is displayed as intended. However, you will find cross-overs between different channels; e.g. channel=domain.com/subdirectory/ and channel=domain.com/subdirectory/subsubdir/ both of these channels will display individual results but the domain.com/subdirectory/ channel will also include the results from domain.com/subdirectory/subsubdir/ The same will apply to various formatted channels; for example, 468x60 and domain.com channels
In the default view, the top line total is web page impressions and the custom channels total is per ad impressions. That is,.... If your custom channel is embedded in all or most all ads on your site. And if you have 3 ads per page. Then your custom channel will report 3 times as many impressions as your entire account. That's because custom channels are always calculated per ad impression (not per page impression). In this case, I assume you have about 2 ads per page and the second entry is a custom channel.